Many systems have been utilized to treat spinal deformities such as scoliosis, spondylolisthesis, and a variety of others. Primary surgical methods for correcting a spinal deformity utilize instrumentation to correct the deformity as much as possible, as well as implantable hardware systems to rigidly stabilize and maintain the correction. Many of these implantable hardware systems rigidly fix the spinal column or allow limited growth and/or other movement of the spinal column, to help facilitate fusion after the column has been moved to a corrected position.